1. Technical Field
The present disclosure relates to a method for reducing noise in a tomographic image acquired by a swept source optical coherence tomography device.
2. Related Art
An optical coherence tomography device (Optical Coherence Tomography: OCT) having an optical interference system and capturing a tomographic image of an object has been known. The optical interference optical system of the device splits a light flux emitted from a light source into a measurement light flux and a reference light flux. The optical interference optical system leads the measurement light flux to the object while leading the reference light flux to a reference optical system. Afterward the optical interference optical system obtains interference light by combining the measurement light flux, which are reflected by the object, and the reference light flux. Furthermore, the optical interference optical system causes a light receiving device to receive the interference light. Such a device is used to obtain a tomographic image (OCT image) of a living organism such as an eyeball or skin.
When a tomographic image of an object is captured by the optical coherence tomography device, noise may occur. An interference signal of the noise is displayed as FPN (Fix Pattern Noise) on the tomographic image. Such noise occurs uniformly on each A-scan line (A-scan).
Hence, when a tomographic image is displayed, the FPN of the tomographic image is reduced, for example, by a noise reduction process (e.g., DC subtraction). In the DC subtraction, the average of a spectrum interference signal (raw data) at each scan position is calculated. Furthermore, an average spectrum corresponding to noise is extracted. The average spectrum corresponding to the noise is subsequently subtracted from the spectrum interference signal (raw data). Consequently, FPN (a signal component unrelated to an interference component) is reduced. As a result, an interference signal related to interference light of the reference light and the measurement light is extracted.
The optical coherence tomography device includes, for example, SS-OCT (Swept Source-OCT) (refer to JP-T-2007-510143). In this device, a wavelength variable light source, which temporally changes an emission wavelength at high speed, is used as a light source. SS-OCT can capture an image at higher speed than known SD-OCT (Spectral Domain-OCT).